1. Field of the Invention
The invention generally relates to optical disk systems and more particularly to a phase lock loop for a controller in an optical disk system and methods therefor.
2. Description of the Related Art
Optical disk systems such as digital versatile disk (DVD), compact disk (CD), DVD-ROM (digital video disk read only memory), DVD−RW, DVD+RW (digital video disk rewritable), CD-ROM and CD-RW are widely used in the art as the storage medium for data. Data are physically stored in the form of pits and lands patterned in a track on the disk. The tracks formed in a spiral line from the inner radius of the disk extending to the outer edge thereof. A pit is a location on the disk where data are recorded by creating a depression on the surface of the disk with respect to the lands. The lands are the areas between the pits in the tangential direction. When storing information on the disk, the length of the pits and lands are controlled according to a predetermined encoding format, such as eight-to-fourteen modulation (EFM). There are other encoding formats in the art suitable for patterning the puts and lands. EFM reduces errors by minimizing the number of zero-to-one and one-to-zero transitions where small pits are avoided. To retrieve information from the disk, light from a laser beam is directed onto the track where the light beam is reflected back to a photo-sensor. Because of different reflectivity in the pits and lands, the amount of reflected light changes at the transitions therebetween. The encoded pattern for the pits and lands modulates the reflected light beam. As the photo-sensor receives the reflected light beam, and outputs a modulated signal that is proportional to the energy of the light in the reflected light beam. In EFM, the data signal includes no less than two zeros and no more than ten zeros between logical transitions at the pit edges. A zero is indicated by no change in the energy of the reflected beam for at least two clock periods. A one is indicated by a change in the energy of the reflected light beam, i.e., a pit edge. Applying EFM, a pit or land includes a length corresponding to the amount of time for at least two and up to ten clock periods where a corresponding voltage is accordingly output.
In EFM encoding, the number of clock periods having a digital value of one should be equal to the number of clock periods having a digital value of zero over a period of time. A clock signal is derived from the digital data signal by a phase lock loop (PLL) in a controller of the optical disk. Provided that the clock includes a clock period T, the EFM signal has digital values of ones and zeroes for integer multiples of the clock period T. A PLL is provided in the controller for each functionality in operating the disk (such as reading and writing information). The PLL ensures proper clock speed in the EFM encoding. For multiple functionalities, such design requirements become cumbersome and inefficient in the art. Significant shortcomings include restrictions in the size and cost of implementation for the controller design of the optical disk.
Thus, there is a general need in the art for an optimally and efficiently designed controller for an optical disk, and more particularly, an optimally and efficiently designed PLL for the controller in an optical disk and associated methods therefor that overcome at least the aforementioned shortcomings in the art.